Liquid crystal display panels have rapidly become one of the most popular types of panels used in a variety of displays, including cell phones, PDAs (personal digital assistants), computer monitors, laptop displays, televisions, and advertising displays amongst others. In a number of cases, it is desirable for an LC display panel to be used outdoor in the sunlight. However, exposure of an LC display panel to sunlight without protection creates serious risk of thermal overload to the panel and vastly reduced lifetime of the display.
In an effort to reduce thermal damage to LC display panels, infrared light blocking films have been applied over LC panels. However, LCD panels absorb mostly in the 400 to 850 nm region of the spectrum with lower absorption at longer wavelengths. Therefore, infrared light blocking films allow some of the most thermally damaging light to pass on to the LC panel. Another approach contemplated is to apply a reflective polarizer to the surface of the LC display panel. However, such an approach undesirably blocks transmission at all angle. Thus, for outdoor viewing in the sunlight, a viewer on-axis will likely only be able to see him or herself and not the display. Applying a matte surface to the LC panel is equally ineffective because this causes very low display contrast due to the bright front surface and may not allow viewing of the image.
For outdoor displays in which an on-axis viewing is contemplated, it would be desirable to have a coating or film applied to the liquid crystal panel that would block a wide spectrum of visible light (as well as infrared light) at off-axis angles, while transmitting a good deal of visible light at on-axis angles, while still blocking both some visible light and infrared light.
One recent invention by 3M Co., disclosed in commonly assigned U.S. patent application Ser. No. 12/696,484 provides for a multilayer optical film positioned on top of a light control privacy film. This invention provides for good off-axis blockage of the light, but also provides for some absorption of light by the light control film absorptive regions on-axis. The invention also does not contemplate utilizing materials for continual use in an outdoor setting. Materials used in continual exposure to direct sunlight often experience UV damage and subsequently perform insufficiently.
It would therefore be desirable to have a display application that could control the sun and heat damage to the LC display panel by blocking a majority of off-axis light, both visible and infrared, and also blocking a portion of on-axis light in the infrared and visible spectrum, while still transmitting a large amount of visible light through at a normal viewing angle to allow for a visible, high contrast image. It would also be desirable if this coating were made up of such materials so as to be capable of the contemplated outdoor use in direct sunlight for extended periods of time. The present description seeks to provide a solution to these needs.